STA1085 datasheet(61/127 Pages) STMICROELECTRONICS

61 / 127 page

DS13319 Rev 2

61/127

STA108x, STA109x

Electrical Characteristics

126

Figure 4. 32.768 kHz Crystal Connection

To drive the 32.768 kHz crystal pins from an external clock source:

–

Bypass mode (for test). Enable the bypass mode (bit XCOSC32K_BYPASS= 1b in

PMU_CTRL register). Apply external single ended clock at M3_SXTALI. Input

clock should be of CMOS level (Low = GND, High = VDDIO_IO_ON)

–

Force Through Mode. Apply external single ended clock at M3_SXTALI. Input

clock should be of CMOS level (Low = GND, High = VDDIO_IO_ON). Clock is

available after OSC startup time.The node M3_SXTALO must not be tied high as

this may cause large current to enter amplifier and damage it permanently.

4.7.3

24 - 26 MHz Oscillator Specifications

The internal oscillator amplifier specifications are shown in Table 26:

COSXTAL

Shunt capacitance

3.5

CLSXTAL

Load capacitance(1)

-22

1. Total capacitance, including board and package parasitics.

Table 25. Typical Crystal Recommended Specifications (continued)

Symbol

Parameter

Limit values

Unit

Min

Typ

Max

32.768 kHz

Crystal

SXTALI

SXTALO

Device

LMSXTAL RMSXTAL CMSXTAL

COSXTAL

Crystal Model

Table 26. Oscillator Amplifier Specifications

Symbol

Parameter

Limit values

Unit

Min

Typ

Max

TMXTAL

Startup Time

3.4

Tduty cycle(Zi &

NZi)

Duty Cycle

AMXTALO

Amplitude of OSCILLATION at MXTALO

0.4

1.6

PSXTAL

Power Consumption during Stable Oscillation

µA

GM0-MXTAL

Transconductance

8.5

15.8

mA/V

Rneg

Negative Resistance

175

285



Frequency Stability

PPM

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